I got this ACOG Trijicon 4x32 ECOS Riflescope for my AR and have been thinking of moving it to the M249. It says M4 and M249 in the bottom of the reticle. The range is somewhat of a question though.

Why does it say M4 100m-600m but the M249 says 700-1000m?

Does that mean I cant use this optic for the BDC on the M249 under 700? Why the heck did they not put 100-1000m if it will work?

The BDC is set for M855 ballistics, “good enough” whether fired from an M4 or M249.

M4 is capable of 500m point - 600m area engagements.

M249 is capable of area target suppression at greater range than M4 because it is a light machine gun providing greater volumes of fire.

I thought I had an ACOG TM laying around somewhere for the “book” explanation. In any case, the scope is designed for use with either system

Agreed.

I believe what the reticle is saying is "Just because you use this on an M4 and the reticle has 800m target lines in it doesn't mean you can hit shit at 800m with your M4.  Your M4 might work to 600m, but the longer range stuff is only useful if you put this on an M249."

But that wouldn't have fit as well...    

Thanks for the guidance guys.